1. Field of the Invention
The present invention relates to a non-directional load detecting sensor for detecting a contact load without being influenced by a load application direction.
2. Description of the Related Art
The foot tip of a walking robot or the finger tip of a robot hand needs to accurately detect a load which acts on the foot or the finger. Any other general machines other than the robots also often need to detect a contact load when their movable member comes in mechanical contact with an external member.
Conventionally, to detect such a contact load, typically a strain gage has been attached to part of the member to thereby measure a change in potential caused by a change in a resistance due to the contact load when they came in contact with each other. Besides, there have been developed also a load cell to which a strain gage is applied and a six-axial tension sensor module for detecting a load application direction.
Those strain gage, load cell, six-axial tension sensor, have the following problems.
(1) The direction of a force that can be detected is limited by a sensor or a direction in which the sensor is attached. In the case of a strain gage or a load cell, it is necessary to know beforehand a direction in which a load acts, so that if that direction does not same with an expected direction, a large error is produced, thus disabling accurate measurement. Moreover, a six-axial sensor can indeed detect a load application direction too but the sensor itself is complicated and large sized.
(2) A strain gage requires a measure of time and labor for its attachment. That is, for accurate measurement it is necessary to attach it using a dedicated adhesive agent, so that measurement is impossible until the agent hardens completely.
(3) A strain gage is not so resistant to an instantaneous excessive force and so its body may be damaged when affected by an excessive shock. More precisely, the gage itself is not damaged by an excessive force but a member attaching the gage is distorted permanently, thus disabling maintaining an accuracy in measurement. Although a load cell or a six-axial tension sensor can use a stopper etc. to prevent an excessive force from being transmitted to an internal sensor (strain gage etc.), its structure is complicated and large sized.
(4) Contact between rigid bodies makes it difficult to model a subject to be controlled. That is, when a rigid portion of the robot comes in contact with a rigid subject such as a floor, a shock is resultantly produced, so that an excessive load periodically has an action instantaneously, thus making it difficult for the robot to model the subject etc. at that moment of contact.
Further, to solve the problems (3) and (4), a spring-component element may be attached to the tip of a load sensor, in which case, however, the sensitivity of the load sensor can be deteriorated.
The present invention is devised to solve the above mentioned problems. That is, it is an object of the present invention to provide such a non-directional load detecting sensor: (1) that can accurately measure a contact load without being influenced by a direction, if changed, of a force to be measured; (2) that can be attached easily so that it can measure a load immediately after being attached; (3) that can well withstand an instantaneous shock load; (4) that can easily model a subject at the time of contact therewith; and (5) that is not deteriorated in sensitivity of its sensor.
The present invention provides a non-directional load detecting sensor comprising an elastic hollow body (2) in which a fluid is filled tightly, a pressure sensor (4) for detecting the pressure of the fluid in the elastic hollow body, and an adapter (6) for coupling the elastic hollow body to an external movable member.
By this configuration of the present invention, a fluid is filled tightly in the elastic hollow body (2), so that when this elastic hollow body comes in contact with an external substance, it is partially deformed to thereby raise the pressure of the fluid contained therein. This rise in pressure in turn can be detected by the pressure sensor (4), thus measuring a contact load. Moreover, by using the adapter to couple the elastic hollow body to an external movable member, the sensor can be easily attached to thereby measure the load immediately. Therefore, this non-directional load detecting sensor can be attached to, for example, the foot tip of a walking robot or the finger tip of a robot hand to thereby accurately detect a load which acts on the foot tip or the finger tip.
Furthermore, a rise in pressure caused by deformation of the elastic hollow body (2) is detected in configuration by the pressure sensor (4) to thereby permit the elastic hollow body to act as a buffer, thus making the sensor well resistant to an instantaneous shock load and exempting it from a deterioration in sensitivity. Moreover, the sensor can easily model a subject when it comes in contact therewith because it is not subject to a rapid change in load such as a shock load.
According to a preferred embodiment of the present invention, the pressure sensor (4) comprises an introducing tube (4a) for introducing a fluid contained in the elastic hollow body and a detecting portion (4b) for detecting the pressure of the introduced fluid, which elastic hollow body (2) is comprised of a hollow sphere portion (2a) having almost a constant wall thickness and a communicating portion (2b) for holding the introducing tube (4a) tightly to communicate the fluid in the hollow sphere body to the introducing tube. The communicating portion (2b) preferably has a larger wall thickness so that it may not be deformed by a change in the pressure of the hollow sphere body (2a).
By this configuration, the spherical hollow sphere portion (2a) can be deformed in proportion to the magnitude of a contact load, thus enabling accurately measuring the contact load without being influenced by the load application direction. In addition, only by inserting the introducing tube (4a) into the communicating portion (2b), it is possible to introduce the internal fluid to the detecting portion (4b) and then measure its pressure with the hollow sphere portion as sealed.
The adapter (6) tightly surrounds the communicating portion (2b) of the elastic hollow body (2) to thereby enhance the fluid-tightness between the introducing tube (4a) and the communicating portion (2b) and also is coupled to part of the hollow sphere portion (2a).
By this configuration, it is possible to enhance the fluid-tightness between the introducing tube (4a) and the communicating portion (2b) to thereby prevent leakage of the internal fluid and also to attach part of the hollow sphere portion (2a) through the adapter (6) to, for example, the foot tip of a walking robot and the finger tip of a robot hand.
Further, the wall thickness and the hardness of the hollow sphere portion (2a) are set so that an external force acting on a semispherical portion of the hollow sphere portion (2a) positioned opposite the communicating portion (2b) may be roughly proportional to an output of the pressure sensor (4).
By this configuration, the contact load (external force) and the output of the pressure sensor (4) are proportional to each other, thus enabling easily knowing a contact load from that sensor output.
The above and other objects, advantages, and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings.